Speed control for patient handling device

ABSTRACT

A patient handling device, such as a bed, stretcher, cot, or the like, includes a motor for driving one or more wheels to assist in the movement of the device. At least one proximity sensor is positioned on the device in order to detect the presence of one or more objects that may lie in the path of the device when it moves. A controller on the device determines the distance between itself and the object and automatically controls the speed of the device in a manner designed to reduce the likelihood of a collision and/or to mitigate the impact of a collision. The automatic speed control of the device may follow one or more predetermined profiles that correlate certain parameters, such as a distance to the object or relative velocity, with a maximum acceptable speed of the device.

BACKGROUND OF THE INVENTION

The present invention relates generally to patient handling devices,such as beds, stretchers, wheelchairs, and the like, and moreparticularly to equipment for assisting in the movement of such devices.

Modern health care facilities utilize a wide variety of patient handlingdevices. Examples of such devices include beds, stretchers, cots,surgery tables, wheelchairs, bed-chairs, and other types of devices thatare designed to help support a patient. Most of these devices includeone or more wheels that enable them to be pushed throughout differentareas of a health care facility, such as a hospital, a nursing home, anassisted living center, or other environments where such devices areused. In some prior art devices, the patient handling devices haveincluded one or more motors that help provide motive force to one ormore of the wheels that move the patient handling device. Such motorsease the load that caregivers and other personnel must exert on thepatient handling device when the device is moved to different locations.

Patient handling devices equipped with motors that assist in themovement of the devices often include one or more controls that arepositioned at one end of the device. When the controls are appropriatelymanipulated, the device starts moving. In order to stop the device, thecaregiver must deactivate the appropriate control. In some situations,the device can be stopped by releasing pressure from a handle, switch,or other safety device that acts as a sort of dead-man's switch. Howeverinitiated, the deactivation often does not cause an immediate stoppingof the device, but rather allows the device to continue to coast forwardand come to a more gradual stop. The gradual stop may allow the patienthandling device to continue forward for a distance greater than thelength of the device. This lack of an immediate stop helps prevent apatient, who may be riding on the device, from experiencing disruptiveacceleration forces.

SUMMARY OF THE INVENTION

The present invention relates to an improved patient handling devicethat includes features that help improve the ease of maneuvering suchpower-assisted devices. In some embodiments, the invention provides apatient handling device that includes one or more proximity sensorspositioned near an end of the device and adapted to prevent or mitigatecollisions with obstacles and/or to help assist in precisely positioningthe patient device at a desired location. The proximity sensor(s) are incommunication with a controller that automatically makes any necessaryspeed adjustments to reduce the likelihood of, and/or severity of, acollision between the device and another object.

In one embodiment, a patient handling device is provided that includes aframe, a patient support surface, a plurality of wheels, a motor, apower assist control, a sensor, and a controller. The patient supportsurface is adapted to at least partially support a weight of a patientpositioned on the patient handling device. The plurality of wheels allowthe patient handling device to be wheeled to different locations. Themotor drives at least one of the wheels. The power assist control ispositioned adjacent a first end of the frame and is adapted to beactivated, such as by pushing or other means, by a person. The sensor issupported by the frame and detects objects within a proximity to thepatient handling device. The controller is in communication with thepower assist control, the motor, and the sensor. The controller isadapted to drive the motor in a manner based upon both the activation ofthe power assist control and the sensor detecting an object within theproximity to the patient handling device.

In another embodiment, a method of controlling a motor adapted to driveat least one wheel on a patient handling device is provided. The methodincludes providing a sensor on the patient handling device that detectsobjects within a proximity of the patient handling device; providing apower assist control on the patient handling device that is adapted tobe activated by a person; driving the motor in a manner to cause thepatient handling device to move forward when a person activates thepower assist control; monitoring the sensor to determine if an object isdetected by the sensor; and, if an object is detected, determining adistance from the patient handling device to the object andautomatically adjusting the motor in such a manner that the patienthandling device will reduce its speed even if the person continuesactivating the power assist control.

According to another embodiment, a method of controlling a motor adaptedto drive at least one wheel on a patient handling device is provided.The method includes providing a sensor on the patient handling devicethat detects objects within a proximity of the patient handling device;providing a power assist control on the patient handling device that isadapted to be activated by a person; driving the motor in a manner tocause the patient handling device to move forward when a personactivates the power assist control; monitoring the sensor to determineif an object is detected by the sensor; and, if an object is detected,automatically controlling an absolute speed of the device to match apredetermined speed profile.

According to still another embodiment, a method of controlling a motoradapted to drive at least one wheel on a patient handling device isprovided. The method includes providing a sensor on the patient handlingdevice that detects objects within a proximity of the patient handlingdevice; providing a power assist control on the patient handling devicethat is adapted to be activated by a person; driving the motor in amanner to cause the patient handling device to move forward when aperson activates the power assist control; monitoring the sensor todetermine if an object is detected by the sensor; and, if an object isdetected, determining a speed of the object relative to the patienthandling device in a direction oriented parallel to a direction ofmovement of the patient handling device.

According to another embodiment, a patient handling device is includedthat includes a frame, a patient support surface, plurality of wheels, amotor, a power assist control, at least one sensor, and a controller incommunication with the power assist control, the motor, and the sensor.The patient support surface at least partially supports a weight of apatient positioned thereon. The wheels allow the patient handling deviceto be rolled to different locations. The motor drives at least one ofthe wheels. The power assist control is positioned adjacent a first endof the frame and may be activated by a user. The sensor is supported bythe frame and detects objects within a proximity to the patient handlingdevice. The controller drives the motor in a manner based upon arelative velocity between the patient handling device and an objectdetected by the sensor.

According to still other embodiments, the controller on the patienthandling device may be configured to reduce a speed limit for the motorwith increasing closeness of the object to the sensor. The controllermay also accelerate the patient handling device, as appropriate, tofollow the speed profile. The sensor may be positioned at a first end ofthe patient handling device and the power assist control may bepositioned at an opposite end. The patient handling device may furtherinclude a speed sensor adapted to detect an absolute speed of thepatient handling device and communicate the absolute speed to thecontroller wherein the controller controls the speed of the motor in amanner based at least partially upon the absolute speed of the patienthandling device. The patient handling device may further includemultiple siderails positioned on opposite sides of the frame, as well asa lifting device adapted to raise and lower the patient support surface.The device may further include four or more cantered wheels and at leastone non-castered wheel, the latter being driven by the motor. Thecontroller may also be in communication with a brake and the controllermay activate the brake in order to carry out the desired speed control.The patient handling device may further include sensors that detect aweight of a patient supported on the patient support surface and thecontroller may use this weight information in controlling the speed ofthe motor when an object is detected. An actuator may also be providedon the patient handling device that raises and lowers the one or moredriven wheels into and out of contact with the floor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one type of patient handling device towhich the various aspects of the invention may be applied;

FIG. 2 is a perspective, exploded view of a power assist control of thepatient handling device of FIG. 1;

FIG. 3 is another perspective, exploded view of the power assist controlof FIG. 2;

FIG. 4 is a rear, elevational view of the power assist control of FIG.2;

FIG. 5 is a partial, perspective view of an alternative power assistcontrol for a patient handling device;

FIG. 6 is a close-up partial perspective view of a sensor andsurrounding components of the power assist control of FIG. 5;

FIG. 7 is a plan view diagram of a patient handling device according toone embodiment;

FIG. 8 is an elevational schematic diagram of a proximity sensor thatmay be used with the patient handling devices of FIGS. 1 and 5;

FIG. 9 is a chart illustrating a plurality of speed profiles forcontrolling the speed of the patient handling device based upon adistance to a detected object;

FIG. 10 is a chart illustrating an illustrative discrete speed profilethat may be followed, in some embodiments, by the patient handlingdevice; and

FIG. 11 is another chart illustrating another speed profile that may befollowed in some embodiments by the patient handling device.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A patient handling device 20 according to one embodiment is depicted inFIG. 1. In the embodiment illustrated, patient handling device 20 is astretcher adapted to support a patient in a health care setting, such asa hospital, clinic, assisted living home, or other environment where theuse of stretchers is beneficial. Patient handling device 20 may take ona variety of different forms, including beds, cots, wheelchairs, surgerytables, or any other type of device adapted to support a patient in ahealth care setting. One example of an alternative patient handlingdevice 20 is partially illustrated in FIG. 5. Other alternative designsmay also be used.

Patient handling device 20 includes a patient support surface 22 onwhich a patient may sit or lie (FIG. 1). Support surface 22 may includea mattress 24 positioned thereon, or some other type of cushioningstructure to provide a more comfortable surface on which a patient maybe positioned. Patient support surface 22 is supported by a top portion26 of a frame 28. Frame 28 includes a base 30 and a pair of liftingmembers 32. Lifting members 32 are each configured to adjustably movetop portion 26 vertically up and down. That is, lifting members 32 areeach configured to move top portion 26 in a direction indicated bydouble-headed arrow 34. Such lifting may be carried out by hydrauliccontrols, electrical controls, or other means. Base 30 of patienthandling device 20 includes a plurality of undriven, castered wheels 36that each may be positioned generally near the four corners of base 30.

Top portion 26 of frame 28 may include a plurality of independentlypivotable sections 38 that allow a patient lying on mattress 24 to havetheir posture adjusted. For example, in the patient handling device 20illustrated in FIG. 1, top portion 26 includes an upper section 38 a,often referred to as a Fowler section, positioned in the region wherethe torso of a patient's body would lie. Upper section 38 a is pivotableabout a horizontal pivot axis that is oriented generally perpendicularto the longitudinal extent of patient handling device 20. The pivotingof upper section 38 a enables a patient to switch between lyingcompletely flat on support surface 22 and sitting up with his or hertorso nearly vertical, as well as variations in between. Patienthandling device 20 may further include one or more lower sections 38 bthat may be pivotable about horizontal pivot axes, such as a knee gatch,and/or other pivotable or non-pivotable sections. Such additionalpivotable sections 38, if any, allow the orientation of the patient'sthighs and/or legs to be changed from a purely flat orientation toraised orientations.

Patient handling device 20 further includes one or more handles 40positioned at a head end 42 of device 20. In the illustration of FIG. 1,only a single handle 40 is visible in the nearest corner of the head end42. However, the embodiment depicted in FIG. 1 includes another handle40 that is positioned in the far corner of head end 42. This otherhandle is visible in FIGS. 2-4. In other embodiments, only a singlehandle 40 may be provided, or a handle that is attached at two differentattachment points may be provided in still other embodiments. In theembodiment of FIG. 5, patient handling device 20 includes only a singlehandle 40 that extends from a first side 54 to a second side 56 ofdevice 20. Further detail about the operation of handle 40 in FIG. 2 isprovided below, as well as in commonly assigned U.S. Pat. No. 6,772,850issued to Waters et al, and entitled POWER ASSISTED WHEELED CARRIAGE,which was filed on Jan. 21, 2000, and the complete disclosure of whichis hereby incorporated herein by reference. Other types of handles mayalso be used, as well as other types of structures that perform afunction similar to that of handle 40, as described below.

Regardless of the specific configuration of handle(s) 40, they may begrasped by a caregiver and used to push and/or pull patient handlingdevice 20 such that it may be wheeled to a different location. Patienthandling device 20 is equipped with a motor 44 (FIG. 7) that drives oneor more drive wheels 46. Motor 44 is activated by a user pushing orpulling on handles 40 and thereby activating one or more handle sensors52 (FIGS. 3-4 and 6-7). Handle sensor 52 is configured such that when auser pushes on handles 40 toward a foot end 48 of patient handlingdevice 20, motor 44 powers drive wheels 46 in a manner causing patienthandling device 20 to move in a forward direction 76 (FIG. 1). When auser pulls on handles 40 toward head end 42, handle sensor 52 mayactivate motor 44 such that it powers drive wheels 46 in an oppositedirection, thereby causing patient handling device 20 to move rearward.Handle 40 and handle sensor 52 thus act together as a power assistcontrol 53 and motor 44 acts as a power assistance device by providingmotive force for moving patient handling device 20 to new locations,thereby reducing the amount of force that a caregiver must exert whenpushing or pulling device 20. Motor 44 therefore helps reduce theworkload of caregivers who are tasked with transporting devices 20 tonew locations.

FIGS. 2-4 illustrate one suitable construction of a power assist control53 that may be used with patient handling device 20, although otherconstructions are possible. Each handle 40 is physically coupled to ahorizontal pivot bar 57 that is rotatable about a horizontal pivot axisX. When a user pushes on either of handles 40 in forward direction 76,the movement of handles 40 causes pivot bar 57 to rotate. This rotationcauses a weldment 59 positioned generally near the center of pivot bar57 to exert a force on handle sensor 52. In the embodiment shown inFIGS. 2-4, handle sensor 52 is a load cell that detects the forcesexerted on it due to the movement of weldment 59. As shown in FIGS. 3-4,a sensor cable 61 transmits the forces detected by sensor 52 to aprinted circuit board assembly (PCB) 63. PCB assembly 63 may contain acontroller 58 that carries out the functions described below, or PCBassembly 63 may be an intermediary component which forward signals ontocontroller 58, which may be located at another suitable location onpatient handling device 20.

The configuration and location of handle sensor 52 and the manner inwhich handles 40 control the movement of motor 44 may be varied in anysuitable manner. In lieu of a load cell, handle sensor 52 may compriseone or more capacitive sensors, pressure sensors, resistance sensors,mechanical sensors, or other types of sensors. Handle sensor 52 may alsobe placed in locations other than as shown in FIGS. 2-4. In theembodiment shown in FIG. 6, handle sensor 52 is a potentiometer whoseresistance changes in response to rotation of a gear 55. Gear 55 isrotated in response to the rotation of handle 40 about horizontal pivotaxis X (FIG. 5-6). The movement of handle 40 thereby causes a change inthe resistance of potentiometer, which is electrically communicated tothe controller 58 on the patient handling device 20 (FIG. 4). Controller58 may take on any suitable form and may be a microprocessor, a fieldprogrammable gate array (FPGA), an application specific integratedcircuit (ASIC), discrete circuitry, a microcontroller, or other suitableelectronic hardware, firmware, and/or software, or any suitablecombination of these or other components. However configured, controller58 is in communication with motor 44 and controls motor 44 such thatpatient handling device 20 moves forward when handle 40 is pushedforward (as would be sensed by sensor 52), and the patient handlingdevice moves backward when the handle is pulled backward (as would besensed by handle sensor 52). The speed at which the patient handlingdevice moves in response to the movement of the handle 40 may bedirectly proportional to the amount of rotation of the handle, or it maybe correlated in another manner besides direct proportionality, such asby a plurality of discrete speeds, an exponential correlation, or inother manners.

In the embodiments of FIGS. 1-6, each of the handles 40 of patienthandling device 20 include a safety switch 50. Safety switches 50 act asa sort of dead man's switch. That is, at least one of the safetyswitches 50 must be continuously activated, such as by pushing by auser, in order to allow the powered assistance of motor 44 to takeplace. Stated alternatively, the pressing of safety switches 50 is anecessary, though not complete, precondition for making motor 44operate. It is not a complete precondition because motor 44 will notdrive any of drive wheels 46 unless handle 40 is also pushed forward, orpulled backward, thereby activating one or both of handle sensors 52.Thus, a user wishing to have patient handling device 20 move forward viathe power of motor 44 must first press at least one safety switch 50 andthen push forward on handle 40 to activate the associated handle sensor52. If the person merely pushes forward on handle 40 and activates oneof the handle sensors 52 without also pressing a safety switch 50, thenmotor 44 will not drive any of drive wheels 46. Thus, a person whopushes forward on handle 40 and activates handle sensor 52 without alsopressing a safety switch 50 will have to manually supply all of thenecessary force to get the wheels on patient handling device 20 to turnwithout any assistance from motor 44.

In some embodiments, only a single one of safety switches 50 needs to bepushed in order to enable the use of motor 44. That is, if a personpushes on only a single one of safety switches 50, motor 44 will beenabled such that any forward pushing the respective handle 40 (assensed by sensors 52) will cause motor 44 to drive the drive wheels 46.If a person stops pressing the single pressed safety switch 50 duringthe transport of patient handling device 20, then motor 44 will stopsupplying motive force to drive wheels 46, regardless of whether or nothandle sensor 52 continues to be activated by the person's continuedpushing. Thus, the release of safety switches 50 will stop the drivingof drive wheels 46 and override any drive signals that are beinggenerated by handle sensors 52. In other embodiments, patient handlingdevice 20 can be configured such that both of safety switches 50 need tobe pressed in order to activate motor 44. In such embodiments, if aperson stops pressing either one of safety switches 50, motor 44 willstop supplying motive force to drive wheels 46 regardless of whether ornot either of handle sensors 52 continue to be activated by the person.

Safety switches 50 may be implemented in a variety of different physicalmanners, including, but not limited to, buttons, levers, capacitivesensors, pressure sensors, or any other type of sensor that is capableof detecting a user's continued intent to utilize motor 44 fortransportation assistance of patient handling device 20. Each safetyswitch 50 may forward its electrical signals to PCB assembly 63 via asafety switch cable 65 (FIGS. 3-4), which then forwards the signal tocontroller 38, or cable 65 may connect directly to controller 58.

It will be understood by those skilled in the art that, although powerassist control 53 has been described herein as comprising one or morehandles 40 and one or more corresponding handle sensors 52, the makeupof power assist control 53 can be varied. For example, one or both ofhandles 40 could be replaced by a one or more levers, buttons, pedals,touch-pads, joysticks, or other suitable devices which can be activatedby a user in order to command patient handling device 20 to move.Further, the one or more sensors 52 can be suitably modified accordingto the particular type of device used to command patient handling device20 to move. Further, power assist control 53 may or may not include anysafety switches 50 or sensors 52. Power assist control 53 can thereforebe implemented in any suitable form that provides an indication to acontroller to control the operation of motor 44.

Patient handling device 20 may be configured to either include only asingle drive wheel 46 or to include multiple drive wheels 46. An exampleof a patient handling device having two separate drive wheels 46 isillustrated in FIG. 7. When configured with two drive wheels 46, onedrive wheel 46 may be positioned along a first side 54 of device 20, andthe other drive wheel 46 may be positioned along a second side 56opposite to first side 54. Further, when equipped with dual drive wheels46, patient handling device 20 may be configured such that theactivation of a single safety switch 50, along with a single handlesensor 52, both of which may be positioned on first side 54 of device20, may cause power to be supplied to only the drive wheel 46 on thefirst side 54 of the device 20. Stated alternatively, supplying power todrive wheel 46 on first side 54 of device 20 may be accomplished by onlyactivating the safety switch 50 and a handle sensor 52 that is alsolocated on first side 54. In such cases, the activation of the safetyswitch 50 and handle sensor 52 on second side 56 of device 20 will causethe drive wheel 46 on the second side 56 to be powered. Such aconfiguration may allow a person to more easily steer patient handlingdevice 20. If it is desirable to turn the device rightward, the personmay push only on the left handle 40 (along with the left switch 50 andsensor 52) to cause only the left drive wheel 46 to rotate. The rotationof only the left drive wheel 46 will tend to push the device 20rightward because off of the off-center location of the left drive wheel46. To turn the device leftward, the person would push in a similarmanner only against the right handle 40 (and right switch 50 and sensor52), thereby driving only the right drive wheel 46. To move the device20 straight forward, the person would push on both of the right and lefthandles 40 simultaneously (along with their respective switches 50 andsensors 52).

When patient handling device 20 is configured such that the two drivewheels 46 may be activated independently of each other, device 20 may beconstructed to include multiple motors—one for each drive wheel.Alternatively, patient handling device 20 might include a single motortied to independent transmissions, or other independent structures thatallow for the individual control of each drive wheel 46.

In other embodiments where there are multiple drive wheels 46, patienthandling device 20 may be constructed such that there is a single sensor52. In such cases, both drive wheels 46 will be activated anddeactivated simultaneously by the action of power assist control 53. Thesimultaneous activation and deactivation of drive wheels 46 may becarried out regardless of whether a person presses or releases only asingle one of safety switches 50.

The signals from the one or more safety switches 50 and handle sensors52 are communicated to controller 58 positioned on-board patienthandling device 20. Controller 58 may be comprised of one or moremicroprocessors, discrete logic circuits, ASICs, FPGAs, embedded logicunits, or any other suitable electronic circuitry or electroniccomponents suitable for carrying out the control algorithms discussedherein, as would be known to one of ordinary skill in the art.Controller 58 is in communication with motor 44 and transmits theappropriate signals to motor 44, or to an intermediate motor controller,that cause motor 44 to respond in the manners described herein.Controller 58 is configured such that the amount of electrical powerthat is delivered to motor 44 can be controlled. This allows controller58 to cause motor 44 to generate a torque and to cease the generation ofthe torque, as well as to control the amount of torque applied. One ormore speed sensors 72 may be included that sense the speed, and/or otherparameters, of motor 44 and feed such information back to controller 58such that the speed, or other characteristics, of motor 44 may becontrolled in a closed-loop manner (FIG. 7). In alternative embodiments,motor 44 may also be controlled by controller 58 in an open loop manner.In some embodiments, patient handling device 20 may be configured suchthat motor 44 never moves drive wheels 46 at speeds in excess of certainpredefined limits. The limits may be different depending upon thedirection in which patient handling device 20 is being moved. Forexample, controller 58 may be configured to limit the forward speed ofdrive wheels 46 to an approximate walking speed, such as 3.0 to 4.0miles per hour, and controller 58 may be further configured to limit thereverse speed of drive wheels 46 to a slower speed, such as 1.0 to 2.0miles per hour. Other speed limits, or no speed limits at all may, ofcourse, be used. Such speed limits refer to limits that are imposed whenno obstruction is detected in the path of device 20 and, as will bediscussed below, such limits may be overridden by other speed controlswhen an object in the path of device 20 is detected.

Whatever the precise value of the speed limits that may be used, if any,patient handling device 20 may be configured such that a person can pushor pull device 20 faster than the speed limits if the person manuallysupplies the requisite motive force to the device 20. That is, if aperson pushes on patient handling device 20 while also causing motor 44to power drive wheels 46, it may be possible for the patient handlingdevice 20 to exceed the programmed speed limit, depending upon how muchforce the person manually applies to device 20. In other embodiments,controller 58 and motor 44 may be configured such that motor 44 activelyresists any manual pushing on device 20 that would cause device 20 toexceed the set speed limits. In this latter embodiment, motor 44 wouldreact to a person pushing on device 20 that was already traveling at thespeed limit by reducing the power to motor 44 such that device 20 didnot exceed the speed limit, or by activating one or more brakes ondevice 20, or, in certain situations, by applying a reverse torque todrive wheels 44. Other variations are also possible.

Patient handling device 20 includes one or more proximity sensors 60(FIGS. 1 and 7) positioned generally near the foot end 48 of device 20.As will be discussed in greater detail below, proximity sensors 60 areused in conjunction with controller 58 to help automatically reduce thelikelihood and/or severity of collisions of patient handling device 20with objects 64, such as walls, corners, equipment, personnel, and othertypes of objects. In the embodiment illustrated in FIG. 1, device 20 isshown with two proximity sensors 60 attached at a foot end of base 30.It will be understood by those skilled in the art that the number ofproximity sensors can be varied from that shown in FIG. 1. In someembodiments, only a single proximity sensor 60 may be used. In otherembodiments, an entire array of proximity sensors 60 may be mounted tothe foot end 48 of device 20. It will also be understood that theposition of proximity sensors 60 may be varied from that shown inFIG. 1. That is, instead of mounting proximity sensors 60 to base 30,they might alternatively be mounted to top portion 26 of frame 28, or toboth top portion 26 and base 30.

Regardless of the position and number of proximity sensors 60 in aparticular embodiment of patient handling device 20, each proximitysensor 60 functions to detect the presence of one or more objects 64within a vicinity 68 (FIG. 7) of the proximity sensors 60. Theconstruction of proximity sensors 60 may take on any of a variety offorms, including, but not limited to, an ultrasonic sensor, a capacitivesensor, a photoelectric sensor, an inductive sensor, a camera, or amechanical sensor. Such sensors are known to those skilled in the art.In general, many of these sensors operate in a manner in which a wave 62is emitted from the proximity sensor 60 in a forward direction 76 withrespect to the patient handling device 20 (FIG. 8). As noted above, theemitted wave may be an ultrasonic wave, an electromagnetic wave, orother type of wave. Upon encountering an object 64 within a certainvicinity to the proximity sensor 60, a portion of the emitted wave 62 isreflected back towards the patient handling device 20 by the object 64.Proximity sensors 60 may each include sensors for detecting thereflected wave 66. In some embodiments, the device for emitting the wave62 may be physically separate from proximity sensors 60. For purposes ofdescription herein, proximity sensors 60 will be hereafter described ascontaining both the emitters and the sensors for detecting the reflectedwaves 66, although it will be understood by those skilled in the artthat the sensors may be physically separated from the structure(s) thatemit the emitted waves 62, and that the following discussion is notmeant to imply that a common structure must be used for both emittingand detecting waves.

Wherever positioned, the proximity sensors 60 detect the reflected waves66 and use information regarding the reflected waves 66 to determine adistance D of the object 64 from patient handling device 20 (FIG. 7).The manner in which the proximity sensors 60 detect distance D may bebased upon any known techniques, such as by measuring the time-of-flight(TOF) of the emitted wave to travel from the proximity sensors 60 to theobject 64 and back, multiplying that time by the expected speed of thewave, and then dividing by two (to account for the fact that the wavetravels both to and from the object 64). Another technique may includemeasuring the amplitude of the reflected waves 66 and comparing thatamplitude to the amplitude of the emitted waves 62 and using anattenuation conversion factor to determine the distance D to object 64.Another technique may include a combination of the TOF measurements andamplitude measurements. Still other techniques may also be used.

Proximity sensors 60 are arranged in both their numbers and theirphysical location, as well as their operational design, to detectobjects within a certain proximity 68 to patient handling device 20(FIG. 7). The size, location, and shape of proximity 68 may be varied indifferent embodiments. In the embodiment illustrated in FIG. 7,proximity 68 is positioned adjacent foot end 48 of patient handlingdevice 20 and extends for a length L and width W. Width W may begenerally about the same as the width of patient handling device 20;that is, it may generally be close to the distance from first side 54 ofdevice 20 to second side 56 of device 20. In other embodiments, it maybe helpful to make width W noticeably smaller than the width of device20 in order to reduce the likelihood of objects to the side of device 20impacting the speed control of device 20. In other embodiments, width Wmay be set somewhat larger than the width of patient handling device 20so that objects that are not directly in front of device 20 may bedetected. This may mitigate collision dangers if patient handling device20 turns as it moves forward. In some embodiments, the size of width Wmay range from two feet to six feet, although values outside theseranges may of course also be used.

As noted, in other embodiments, the width W may be set smaller than thewidth of patient handling device 20 with the expectation that the personcontrolling device 20 will steer it to avoid objects that may onlypartially lie in the forward path of patient handling device 20. Instill other embodiments, patient handling device 20 may be constructedsuch that the width W of proximity 68 may be variable, including avariability that automatically adjusts to a larger value upon detectingthat device 20 is turning and automatically returns to a lower valuewhen device 20 is traveling straight. The width W of proximity 68 mayalternatively be controller by the user of device 20 by one or morecontrols positioned on device 20. Still other variations are possible.

The length L of proximity 68 may generally be equal to or greater thanthe expected braking distance of patient handling device 20. That is,length L of proximity 68 may be set such that, at a minimum, it is atleast equal to the distance that device 20 would typically travel whendecelerating from its highest speed limit to a stopped condition. Suchdeceleration may include active braking, or such deceleration mayinclude cutting off power to motor 44, in which case the device 20 wouldsimply coast to a stop. Length L may also be much greater than theminimum expected stopping distance of device 20, including multiples ofthis distance. In some embodiments, length L may range from 10 to 15feet, although it will be understood that other values for Length L maybe used. Indeed, in some embodiments, the length L may be variable, andpatient handling device 20 may be configured to take into account theweight of device 20 in determining the length L. In such embodiments,the length L may be increased when device 20 is occupied, due to thegreater mass and greater required braking distance, and length L may bedecreased when not occupied. Patient handling device 20 may include oneor more weight sensors 88 (FIG. 7), such as load cells or the like, thatmeasure the weight of a patient and/or other equipment supported ondevice 20, and device 20 may be configured to utilize this weightinformation to dynamically adjust length L. Still other variations arepossible.

The width W and length L may be set by the choice of proximity sensors60, their position, and/or the number of sensors utilized. Either orboth of these variables may also be set by the particular manner inwhich the reflected waves 66 are processed. For example, the length Lmay be set by ignoring any detected reflected waves 66 that have atime-of-flight that corresponds to a distance greater than the selectedlength L. The width W may also be set through processing algorithms, forexample, by processing only those components of reflected waves 66 thatare detected within a specified angular range when directionallysensitive proximity sensors 60 are used. Other algorithms may also beused to control the width W and length L of proximity 68.

When viewed from above, such as shown in FIG. 7, the shape of proximity68 is generally rectangular, although the boundaries of proximity 68 maybe more curved than that illustrated in FIG. 7. The precise plan viewshape of proximity 68 may be varied from that shown in FIG. 7 and maydepend upon the type and/or arrangement of the one or more sensors 60.When viewed from the side (the elevational view), the shape of proximity68 may also be generally rectangular, although it may be other shapes aswell, such as fan-shaped, or other shapes. In some embodiments,proximity sensors 60 may be positioned at multiple positions on patienthandling device 20 that are vertically separated from each other. As butone of multiple possible examples, one or more proximity sensors 60 maybe positioned on base 30 while one or more proximity sensors 60 may bepositioned on top portion 26 of frame 28. In general, the shape and sizeof proximity 68 should be chosen such that proximity sensors 60 have ahigh likelihood of detecting most, if not all, objects 64 for whichcollisions are desirably avoided through automatic control. The shapeand size of proximity 68 may therefore be application and/or environmentspecific.

When the reflected waves 66 are detected by proximity sensors 60, theproximity sensors 60 produce electrical signals that are processed inorder to determine the distance D to the one or more detected objects64. This processing may be carried out by suitable electronic circuitrythat is part of, or positioned near, proximity sensors 60, or it may becarried out by controller 58, or it may be carried out in a dividedmanner with some processing being done locally at proximity sensors 60and some being done at controller 58. Regardless of how the signalscorresponding to reflected waves 66 are processed, controller 58 usesthese signals to determine the distance D to one or more objects 64.This distance D determination is carried out multiple times a second.That is, proximity sensors 60 send out an emitted wave 62 multiple timesa second and “listen” for corresponding reflected waves 66 multipletimes a second. From a comparison of the multiple distance measurementsand the time that elapses between them, controller 58 is able tocalculated the relative speed between device 20 and the object 64.

Controller 58 uses the determination of distances D and the relativevelocity to the objects 64 in carrying out its control of the speed ofmotor 44. More particularly, controller 58 will control the speed ofmotor 44, and thus patient handling device 20, based upon the calculateddistance D and relative velocity to object 64. The precise manner inwhich controller 58 controls the speed of motor 44 based upon distanceand/or relative velocity can be varied widely. FIG. 9 illustrates twodifferent speed profiles 70 a and 70 b for controlling device 20 basedupon the distance D to a detected object. The distance D to the objectis shown along the x-axis of the graph of FIG. 9. The acceptablerelative velocity (ΔV) between patient handling device 20 and the object64 is illustrated along the y-axis of the graph of FIG. 9. Controller 58will send appropriate commands to motor 44 to cause patient handlingdevice 20 to move in such a manner that the maximum relative velocitybetween device 20 and object 64 generally matches a profile stored in amemory 71, such as profiles 70 a, 70 b, or some other speed profile.

FIG. 9 illustrates two different suitable speed profiles 70 a and 70 bthat controller 58 may follow in carrying out its speed control ofdevice 20. Speed profiles 70 a and 70 b overlap in the range of 1-2miles per hour, as well as the range of 10 to 14 miles (and above). Inthe range of 2 to 10 miles per hour, speed profiles 70 a and 70 bdiffer, with speed profile 70 a having a linear variation and speedprofile 70 b having a non-linear variation. Other speed profiles may beused having different shapes than those illustrated by profiles 70 a and70 b. Other speed profiles may also be used that have differenttransition points at which the speed limit changes occur besides the 2mph and 10 mph transition points shown in FIG. 9. Speed profiles 70 aand 70 b override the other speed limits that were discussed above(where no object is detected) in relation to handle sensors 52. That is,if handle sensors 52 allow a maximum speed of 4 miles per hour (when noobject is detected), but the particular speed profile specifies amaximum speed limit of 3 miles an hour when an object is detected,controller 58 will limit the speed to 3 miles per hour when an object isdetected.

If a patient handling device 20 includes a controller 58 that followsspeed profile 70 a, then controller 58 will allow the device 20 tocontinue to travel at its maximum speed of 4.5 miles per hour as long asany stationary objects detected by proximity sensors 60 are at least tenfeet away from device 20 (i.e. D is greater than or equal to 10 ft). Ifthe object 64 is non-stationary and moving toward device 20 at anon-zero speed, then controller 58 will limit the speed of device 20such that its relative velocity to the object is no more than 4.5 mph(assuming a distance of 10 ft or greater). If an object is detected thatfalls within the range of 2 to 10 feet, the controller 58 willautomatically set the maximum speed of patient handling device 20according to the profile 70 a shown in FIG. 9. Thus, for example, if anobject is detected at five feet, then controller 58 will set the maximumspeed of patient handling device 20 such that the relative speed betweendevice 20 and object 64 is not more than approximately 2 miles per hour.In such a case, if the object is moving away from device 20, theabsolute speed of device 20 (i.e. speed with respect to the ground) mayexceed 2 mph. Thus, it would be possible, for example, for device 20 tobe traveling at 4.5 mph while a person (e.g. object 64) was only threefeet in front of device 20, provided that the person was walking in thesame direction as device 20 with sufficient speed so as to not exceedthe relative speed limit of profile 70 a (or whatever other speedprofile was being followed).

If a patient handling device 20 includes a controller 58 that followsspeed profile 70 b, then controller 58 will also allow the device 20 tocontinue at its maximum speed of 4.5 miles per hour as long as anystationary objects detected by proximity sensors 60 are at least tenfeet away from device 20. For mobile objects 64, controller 58 may slowdown device 20, depending upon the direction of movement of the mobileobject. If an object is detected that falls within the range of 2 to 10feet, the controller 58 will automatically set the maximum speed ofpatient handling device 20 such that the relative speed matches theprofile 70 b shown in FIG. 9. Other profiles may be used, including, butnot limited to, discrete speed profiles, such as speed profile 70 cillustrated in FIG. 10.

The speeds identified by profiles 70 a-c are, as noted above, maximumspeeds. In other words, patient handling device 20 may be controlled viahandle sensor(s) 52 (and safety switch(es) 50) to operate with relativespeeds less than those indicated in profiles 70 a-c, or whatever othertype of speed profile that may be used for device 20. For example, if aperson is pushing on handles 40 of patient handling device 20 with anamount of force that causes controller 58, via motor 44, to drive device20 forward at a speed of two miles per hour, and if the proximity sensor60 detects a stationary object at a distance D of eight feet, thencontroller 58 will not undertake any actions that change thethen-current speed of device 20 (when following any of profiles 70 a-c).Instead, controller 58 will prevent device 20 from moving any fasterthan about 3.5 miles per hour for profile 70 a, or about 4.25 miles perhour for profile 70 b, or 2.5 mph for profile 70 c. As a result, if aperson increases their pushing force on handle sensors 52 to such anextent that controller 58 would otherwise increase the speed of device20 to 4.5 miles an hour, controller 58 will override the control signalsfrom handle sensors 52 such that the maximum relative speed specified byprofiles 70 a-c (or another profile) are enforced.

The manner in which controller 58 controls the speed of motor 44 andcarries out the necessary speed commands to effectuate the chosen speedprofile may be varied in accordance with multiple different knowntechniques. As but one example, controller 58 may control motor 44through the use of pulse-width-modulated signals (PWM), such asdescribed in U.S. Pat. No. 6,772,850, where the duty cycle of the PWMsignal is correlated to the amount of electrical power supplied to motor44. Motor 44 can therefore be controlled to operate at a desired speedthrough the selective alteration of the duty cycle of the PWM controlsignals. Other types of control techniques may also be used, as would beknown to those skilled in the art. Whatever the precise technique usedto control the speed motor 44, it may utilize known closed loop feedbackprinciples involving one or more sensors that detect the speed, or othercharacteristics, of motor 44 and which feed their signals back tocontroller 58. The degree of fidelity to which the relative speed ofdevice 20 matches the particular speed profile utilized can vary and itis not necessary to precisely match the chosen speed profile. Motor 44may take on the form of any known type of motor suitable for use withpatient handling devices, including, but not limited to, a directcurrent (dc) motor, an alternating current (ac) motor, a frequencycontrolled motor, a brushless motor, a brushed motor, a three-phasemotor, or other types of motors.

The type of control techniques that are used to implement the selectedspeed profile 70 may be the same control techniques that are used toimplement the speed signals generated as a result of handle sensors 52.In other words, if different forces exerted on handle sensors 52 resultin PWM signals being transmitted to motor 44 (or an associated motorcontroller) that have different duty cycles, then the implementation ofthe selected speed profile may also be carried out by using PWM signalsof variable duty cycles to implement the speed limits of the selectedspeed profile. In such a case, motor 44 will receive a single PWM signal(or its associated motor controller) that specifies the commanded speed.This single PWM signal will have a duty cycle that, unless it isoverridden by controller 58 due to the selected speed profile, will bedictated by the amount of force applied to handle sensors 52. Thus,controller 58 will use the selected speed profile to adjust, ifnecessary, the control signals applied to motor 44 as a result of handlesensor(s) 52.

All of the speed profiles 70 a-70 c shown in FIGS. 9-10 allow for thepatient handling device 20 to continue to move at ½ mile per hour evenwhen an object 64 is detected within a two feet or less of proximitysensors 60. That is, none of speed profiles 70 a-70 e act to completelystop the patient handling device 20 from moving. This allows a personmoving patient handling device 20 to continue to move the device so thatit may be accurately positioned at desired locations relative to anyobject 64 that may be detected, such as walls, other devices, etc. Themaximum speed of device 20 when positioned close to object 64, however,is limited to half a mile per hour so that, to the extent the persondrives the device 20 into the nearby object 64, the resulting impactshould be minimized to the point of having limited, if any, destructiveimpact, either with respect to device 20, the patient thereon, or theobject. As a consequence, for example, if a person is trying to movedevice 20 such that its foot end 48 will abut against a wall, controller58 will still allow the person to continue to move device 20 even afterthe wall become less than 24 inches from the foot end of the device 20.The speed of device 20, however, will be limited such that any eventualcollision with the wall will be minimal.

In other embodiments, the speed profile that is used by patient handlingdevice 20 may be one in which the maximum speed of device 20 does reach0 miles per hour, either at a negligible distance, such as an inch fromobject 64, or at some other cutoff distance. In such embodiments, thesignals from handle sensors 52 will be completely overridden at thecutoff distance so that, for example, if a person continues pushing onhandle sensors 52 while an object is detected that is an inch away,motor 44 will remain stopped. In such situations, a person who wanted tomove device 20 the remaining inch or so further to the object would haveto manually supply all of the motive force necessary to wheel device 20to the desired stopping point.

In other embodiments, patient handling device 20 may be configured tobring device 20 to a stop right at the movement device 20 abuts againstthe object. Such a docking mode would include a speed profile thatshrank to zero mph at a distance D of zero (or very close thereto).Further, the speed profile of the docking mode may reflect an actual,controlled speed of patient handling device 20, rather than a maximumpermissible speed (as with speed profiles 70 a-70 c). The docking modecould occur automatically as an object neared device 20, or a personcould separately initiate the docking mode in any suitable manner, suchas by pressing a button, or otherwise manipulating a control on device20, such as a control located on a control panel near handles 40. In oneembodiment, the docking mode could be entered any time after an objectis detected by proximity sensors 60. Upon entering the docking mode,device 20 would automatically drive itself until it stopped precisely atthe detected object, or at a particular distance therefrom. In someembodiments, this automatic driving could take place even if the personremoves their hand or hands from either or both of handle sensors 52.Thus, if a person wanted to move a patient handling device 20 such thatfoot end 48 was positioned precisely against a wall, for example, theperson could steer the device 20 until sensors 60 detected the wall, (atwhich point a light might flash on a control panel), and then activatewhatever control or controls were necessary to enter the docking mode.Once entered, the user could relinquish his or her hands from the device20 and it would automatically continue to move forward following itsselected speed profile until it stopped adjacent the wall. The dockingmode thus acts as a sort of automatic parking feature for the device 20,enabling personnel to easily position device 20 at desired distancesrelative to objects. The desired distances may be variable and enterableby the user via a suitable control panel on device 20.

Patient handling device 20 may be configured, in some embodiments, todetect the absolute speed of object 64 relative to the ground, or theabsolute speed of device 20 relative to the ground. Controller 58 mayuse either or both of these absolute speed measurements in carrying outits automatic speed control. In one embodiment, controller 58 may useeither or both of these absolute speed measurements to alter the speedprofile 70 which it follows, or to select a different speed profile. Thealteration of the speed profile 70, or the selection of a new speedprofile 70, may be undertaken in order to account for the kinetic energyin device 20 that may otherwise be obscured when relying solely uponrelative speed measurements. In other words, controller 58 may imposemore severe speed limits in situations where it has a higher kineticenergy but the same relative velocity to an object. For example, if therelative velocity between a stationary object 64 and device 20 is 4miles per hour, controller 58 may restrict the speed of device 20 to agreater extent than it would in the situation where a four mile per hourrelative velocity was present but object 64 had an absolute velocitytoward device 20. For example, suppose the object had an absolute speedof 2 mph toward device 20 mph and the device 20 had an absolute speed of2 mph toward the object (thus resulting in a 4 mile per hour relativevelocity). In such a situation, controller 58 may allow a higherabsolute speed limit for device 20 because there is less kinetic energyin device 20 to eliminate or reduce than in the situation where object64 was stationary.

In addition to the speed profiles 70 a-c illustrated in FIGS. 9-10,which correlate a maximum relative speed to a measured distance, speedprofiles that map other variables may also be used. For example, FIG. 11illustrates a speed profile 70 d that maps measured object distancesdirectly to an absolute maximum speed of device 20, rather than arelative maximum speed as in speed profiles 70 a-c. Thus, in the exampleof FIG. 11, controller 58 will direct device 20 to move at a speed of2.5 miles per hour anytime an object is detected within 4-9 feet ofsensor 60, regardless of whether the object is stationary or mobile. Instill other speed profiles, controller 58 may map measured relativespeeds between device 20 and object 64 to maximum absolute speeds fordevice 20. In still other embodiments, speed profile 70 may map stillother parameters in other ways.

Proximity sensor(s) 60 may also be configured, in some embodiments, todetect a lateral distance LD of objects 64 from a longitudinalcenterline 78 of device 20, in addition to their distance D in front ofdevice 20 (FIG. 7). Controller 58 may use the lateral distance LD indetermining how to control the speed of the one or more motors 44. Thatis, the speed profiles illustrated in FIGS. 9-11, which are functions ofdistance, may be modified to be functions of lateral distance LD inaddition to the total distance D. The manner in which controller 58 mayfactor into account the lateral distance values may vary widely, butgenerally may involve lower maximum speed limits the closer a detectedobject 64 is to the centerline 78. The theory behind such reduced speedlimits is that objects directly in front of device 20 (i.e. those on orclose to centerline 78) may be more difficult to steer around than thosefurther away from centerline 78. The maximum speed of device 20therefore may be curtailed in a greater fashion the closer the object isto centerline 78.

In addition to detecting the lateral distance LD of objects 64, patienthandling device 20 may be configured, in some embodiments, to alsodetect a lateral speed of objects 64. The lateral speed of objects 64refers to the speed of the objects 64 in a direction perpendicular tocenterline 78. When patient handling device 20 detects the lateral speedof objects 64, controller 58 may be configured to first determine if thelateral speed of the object 64 is sufficient, assuming no changes aremade to the lateral speed, to cause the object to move out of proximity68 prior to the arrival of patient handling device 20 at the location ofthe object. If controller 58 determines that the lateral speed of theobject is such that it will exit vicinity 68 prior to device 20'sarrival, then controller 58 will not implement any speed limit basedupon the detection of that object, even if the object is at a distance Dthat would otherwise cause a speed limit to be imposed were the objectstationary. In other words, controller 58 may be configured to react toobjects 64 with lateral speeds differently than objects 64 that have nolateral speeds. Such different reactions would allow a person to walkbriefly across the forward path of device 20 without affecting the speedof device 20 provided the person walked with a lateral speed sufficientto bring them out of the direct path of device 20 prior to the arrivalof device 20 at the person's location.

Patient handling device 20 is configured such that if it detectsmultiple objects, it will react to the object that presents the greatestthreat of a collision. For example, if sensors 60 detect a firststationary object at a distance of four feet and a second stationaryobject at a distance of eight feet, and if controller 58 is followingthe speed profile 70 a of FIG. 9, controller 58 will institute a speedlimit of 1.5 miles per hour, which is the speed limit set by profile 70a for a distance of four feet. The manner in which sensors 60 discernmultiple objects from a single object may take on any of variousconventional manners used in other arts, such as radar sensing and otherposition sensing equipment utilizing reflected waves, as would be knownto one skilled in the art.

In carrying out any of the various embodiments discussed herein,controller 58 may utilize one or more brakes 80 (FIG. 7), if necessary,to carry out the appropriate speed controls. That is, in sonicinstances, merely reducing power to motor 44 may not cause device 20 toslow down, such as when traveling down an incline or when using a motorwith freewheeling characteristics. Or, in other instances, merelyreducing power to motor 44 may not cause device 20 to slow down fastenough. In any of these situations, as well as in other situations,controller 58 may apply one or more brakes 80 to reduce the speed adesired amount. The brakes that may be applied by controller 58 may bebrakes for the one or more drive wheels 46, or they may include brakesfor the one or more castered wheels 36 that may be present on device 20.Regardless of whether controller 58 activates brakes 80 on drive wheels46 or castered wheels 36, or both, controller 58 specifies the degree ofbraking that should be applied. In other words, controller 58 is able togenerate intermediate amounts of braking that are less than the fullbraking force that may be applied by brakes 80. This ability to supplyintermediate braking levels allows for smoother control of device 20than would otherwise be possible. The application of the brakes may alsobe triggered at certain threshold distances to objects whereby if theobject gets within a specified threshold distance, controller 58 appliesthe brakes.

In still other embodiments, controller 58 may be in communication with abattery level sensor 82 and/or a power plug sensor 84. Battery levelsensor 82 measures an amount of electrical power that remains in abattery 86 positioned on board device 20 that provides the electricalpower to motor 44. Controller 58 may provide a visual indication tousers of device 20 via one or more control panels, or other displays, ofthe amount of power remaining in battery 86. Controller 58 may alsoprevent the powered movement of device 20 via handle sensors 52 andmotor 44 if the power level in battery 86 falls to too low of a level.Battery 86 is typically a rechargeable battery that is capable of beingrecharged through an electrical cable on-board device 20 that plugs intoan electrical wall outlet when device 20 is not being moved. In order toprevent device 20 from being moved via motor 44 while this cord is stillplugged into a wall outlet, power plug sensor 84 detects when the cordis plugged into a wall outlet and sends a signal to controller 58 ofthat fact. Controller 58 reacts to this by ignoring any motion commandsthat may be sensed by handle sensors 52 and by displaying a visualwarning that indicates that the power cord must first be unpluggedbefore motor 44 can be activated. Controller 58 and power plug sensor 84thereby act to help prevent the power cord from being inadvertently tornfrom the electrical wall outlet.

In some embodiments, patient handling device 20 may be configured tolimit its speed even if a motor 44 is not supplied on device 20. Thatis, some patient handling devices 20 may not necessarily be equippedwith motors for assisting the movement of the device 20, but insteadrely upon an individual manually pushing on device 20 to move it. Suchembodiments may include one or more castered wheels that enable theindividual to wheel the device 20 to its intended location. In suchembodiments, controller 58 acts to limit the speed based upon objectsdetected by proximity sensors 60 in order to reduce the likelihood ofcollision with those objects. Controller 58 accomplishes this speedcontrol through the selective application of one or more brakes 80positioned on device 20. Controller 58 may use any suitable type ofspeed profile in carrying out its collision avoidance, although thespeed profiles for manually powered devices 20 will typically have atransition point 74 at a smaller distance D than a motor-powered device20. The use of speed profiles on manually powered devices 20 can beparticularly useful in situations where it may be difficult for anindividual to manually stop the device 20, such as when traveling downramps or in other situations.

As was noted above, proximity sensors 60 in the various embodimentsdiscussed herein may utilize ultrasonic, electromagnetic, inductive,capacitive, photoelectric, machine vision, or capacitive sensingtechnologies. When implemented as a mechanical sensor, proximity sensors60 may include a physical structure that extends forward from device 20and senses contact with objects in the path of device 20. The physicalstructure may be constructed of a highly flexible material that allowsthe structure to flex upon contact with the object so that the physicalstructure does not itself cause a jarring collision with the objectdetected.

Additional modifications can be made to all of the different embodimentsof patient handling device 20 discussed herein. Some of these additionalmodifications include the repositioning of proximity sensors 60 at headend 42 of device 20 and the repositioning of handles 40 and handlesensors 52 at foot end 48 of device 20. Such repositioning would allowthe device to be pushed from the foot end 48, rather than the head end42. Still further, device 20 could be modified to include handles 40,handle sensors 52, and proximity sensors 60 on both head and foot ends42 and 48, thereby allowing a person to push the device 20 from eitherend while still maintaining the collision avoidance features. In stillother embodiments, the one or more drive wheels 46 may be verticallymovable between an extended position in which they contact the floor anda retracted position in which they disengage the floor. This retractionof the drive wheels may facilitate sideways movement and/or turning ofthe device 20, which may be desirable in certain situations, such aswhen the device 20 is being finally positioned in a particular room orother area. Some embodiments of patient handling device 20, such as thatillustrated in FIG. 1, may include one or more siderails 90 that aremovable between raised and lowered positions.

It should further be understood that, although the bulk of thediscussion above has focused on automatically reducing the speed ofdevice 20 in order to match the selected speed profile 70, controller 58may also automatically accelerate device 20 in certain situations inorder to match the speed profile 70. Such automatic acceleration mayoccur when a detected mobile object 64 accelerates away from device 20,thereby causing at least a temporary decrease in the relative velocitybetween the device 20 and the mobile object 64. If the device 20 wastraveling at a speed less than the permitted maximum of the speedprofile 70 at the moment of the object's acceleration, controller 58 mayautomatically accelerate device 20 (even without any pressure or forcechanges made to power assist control 53). Thus, as but one example, if auser were pushing on (or otherwise activating) power assist control 53at a constant force or pressure and device 20 automatically slowed downdue to the proximity of a person, the speed of device 20 mightautomatically increase back to its original speed if the person movedout of the way of device 20, or if the person accelerated in the samedirection as the movement of device 20.

It will be understood that the embodiments shown in the drawings anddescribed above are merely for illustrative purposes, and are notintended to limit the scope of the invention which is defined by theclaims which follow as interpreted under the principles of patent lawincluding the doctrine of equivalents.

What is claimed is:
 1. A patient handling device comprising: a frame; apatient support surface adapted to at least partially support a weightof a patient positioned on said patient handling device, said patientsupport surface supported by said frame; a plurality of wheels adaptedto allow said patient handling device to be rolled to differentlocations; a motor adapted to drive at least one of said wheels; a powerassist control positioned on said patient handling device, said powerassist control adapted to be activated by a person; a sensor coupled tosaid patient handling device adapted to detect objects within aproximity to the patient handling device; and a controller incommunication with said power assist control, said motor, and saidsensor, said controller adapted to drive said motor such that a speed ofsaid patient handling device follows a predetermined speed profile whileat least one of the objects continues to be detected and said powerassist control continues to be activated, said predetermined speedprofile defining a plurality of acceptable speeds for a range ofdistances between said patient handling device and the at least oneobject.
 2. The device of claim 1 wherein said predetermined profilecorrelates a distance of the object to a relative speed of the deviceand said profile includes only non-zero speeds.
 3. The device of claim 2wherein said speed profile indicates slowing down the speed of the motorat a rate that increases with increasing closeness of the object to thesensor.
 4. The device of claim 1 wherein said speed profile indicatesaccelerating said patient handling device if an increase in distancebetween said patient handling device and the object is detected.
 5. Thedevice of claim 1 wherein said sensor is positioned at a first end ofsaid patient handling device and said power assist control is positionedat a second end of said patient handling device, said second endopposite said first end.
 6. The device of claim 1 further including aspeed sensor adapted to detect an absolute speed of said patienthandling device, said speed sensor in communication with saidcontroller, and said controller further adapted to control a speed ofsaid motor in a manner that takes into account the absolute speed ofsaid patient handling device.
 7. The device of claim 1 wherein saidpatient handling device is one of a bed and stretcher, and said patienthandling device further includes: a first siderail positioned on a firstside of said frame; a second siderail positioned on a second side ofsaid frame, said second side opposite said first side; and a liftingdevice adapted to raise and lower said patient support surface.
 8. Thedevice of claim 7 wherein said plurality of wheels include four casteredwheels and at least one non-castered wheel, said non-castered wheeladapted to be driven by said motor.
 9. The device of claim 1 whereinsaid controller is adapted to drive said motor, when no object isdetected by said sensor at a speed based upon an amount of force exertedby a person on said power assist control.
 10. The device of claim 1further including a brake in communication with said controller whereinsaid controller is further adapted to activate said brake in order tofollow said speed profile.
 11. The device of claim 1 wherein saidpatient handling device includes weight sensors adapted to detect aweight of a patient supported on said patient support surface and saidcontroller is adapted to control a speed of said motor when an object isdetected in a way that is based upon said detected weight.
 12. Thedevice of claim 1 wherein said sensor is configured to detect multipleobjects and said controller is adapted to select one of said multipleobjects and use at least one characteristic about the selected object incontrolling said motor.
 13. The device of claim 12 wherein saidcontroller is adapted to select the one of said multiple objects that islikely to impact the patient handling device the soonest, said selectionbeing based at least upon the speed of the multiple objects and therespective distances of the multiple objects to the patient handlingdevice.
 14. The device of claim 4 wherein said controller allows saidmotor to continue driving said at least one wheel at at least a nominalspeed no matter how close the object gets to said patient handlingdevice, so long as said power assist control remains activated.
 15. Apatient handling device comprising: a frame; a patient support surfaceadapted to at least partially support a weight of a patient positionedon said patient handling device, said patient support surface supportedby said frame; a plurality of wheels adapted to allow said patienthandling device to be rolled to different locations; a motor adapted todrive at least one of said wheels; a power assist control positionedadjacent a first end of said frame, said power assist control adapted tobe activated by a person; a sensor coupled to said patient handlingdevice and adapted to detect objects within a proximity to the patienthandling device; and a controller in communication with said powerassist control, said motor, and said sensor, said controller adapted todrive said motor in a manner based upon a relative velocity between saidpatient handling device and an object detected by said sensor.
 16. Thedevice of claim 15 wherein said controller drives said motor accordingto a predetermined speed profile that correlates a distance of theobject to a relative speed between the object and said patient handlingdevice.
 17. The device of claim 16 wherein said profile includes onlynon-zero speeds.
 18. A patient handling device comprising: a frame; apatient support surface adapted to at least partially support a weightof a patient positioned on said patient handling device, said patientsupport surface supported by said frame; a plurality of wheels adaptedto allow said patient handling device to be rolled to differentlocations; a motor adapted to drive at least one of said wheels; a powerassist control positioned adjacent a first end of said frame, said powerassist control adapted to be activated by a person; a sensor coupled tosaid patient handling device and adapted to detect objects within aproximity to the patient handling device; and a controller incommunication with said power assist control, said motor, and saidsensor, said controller adapted to: (1) drive said motor in a manner tocause said patient handling device to move forward when a personactivates said power assist control, (2) monitor said sensor todetermine if an object is detected by said sensor, and (3) if an objectis detected by said sensor, determine a distance from said patienthandling device to said object and automatically adjust the motor insuch a manner that said patient handling device will reduce its speed,but not completely stop, even if the object continues to get nearer tosaid patient handling device and the person continues activating saidpower assist control.
 19. The device of claim 18 wherein said controlleris further adapted to determine if said object is moving and, if so,determine a direction of movement of said object and use the directionof movement information to control said motor.
 20. The device of claim18 wherein said controller is further adapted to determine if multipleobjects have been detected by said sensor and, if multiple objects havebeen detected, control said motor in a manner intended to avoidcollision with any of said multiple objects.
 21. A patient handlingdevice comprising: a frame; a patient support surface adapted to atleast partially support a weight of a patient positioned on said patienthandling device, said patient support surface supported by said frame; aplurality of wheels adapted to allow said patient handling device to berolled to different locations; a motor adapted to drive at least one ofsaid wheels; a power assist control positioned adjacent a first end ofsaid frame, said power assist control adapted to be activated by aperson; a sensor coupled to said patient handling device and adapted todetect objects within a proximity to the patient handling device; and acontroller in communication with said power assist control, said motor,and said sensor, said controller adapted to: (1) drive said motor in amanner to cause said patient handling device to move forward when aperson pushes on said power assist control, (2) monitor said sensor todetermine if an object is detected by said sensor, and (3) if an objectis detected by said sensor, automatically control an absolute speed ofsaid patient handling device so as to not exceed a predetermined speedprofile.
 22. The device of claim 21 wherein said controller is furtheradapted to automatically apply a brake on the patient handling device,as necessary, in order to not exceed said predetermined speed profile.23. The device of claim 21 wherein said controller is further adapted toautomatically accelerate said patient handling device if the detecteddistance between the object and the patient handling device increases.24. The device of claim 21 wherein said predetermined speed profile mapsobject distances to acceptable speeds between said patient handlingdevice and the object.
 25. The device of claim 1 wherein said patienthandling device is a bed or a stretcher, and said power assist controlincludes at least one handle positioned at an end of said patienthandling device.
 26. The device of claim 15 wherein said patienthandling device is a bed or a stretcher, and said power assist controlincludes at least one handle positioned at an end of said patienthandling device.
 27. The device of claim 18 wherein said patienthandling device is a bed or a stretcher, and said power assist controlincludes at least one handle positioned at an end of said patienthandling device.
 28. The device of claim 21 wherein said patienthandling device is a bed or a stretcher, and said power assist controlincludes at least one handle positioned at an end of said patienthandling device.